The study examines the agreement among raters on children's problematic behaviors. A multitrait-multimethod (MTMM) matrix was applied to a normative sample of elementary school-aged children (N = 841). The participants were rated by their physical educators, using the Motor Behavior Checklist for children (MBC; Efstratopoulou, Janssen, & Simons, 2012). Teachers and parents rated the same students using the Teacher Report Form (TRF; Achenbach, 1991b), the Child Behavior Checklist (CBCL; Achenbach, 1991a) and the ADHD Rating Scale-IV (DuPaul, Power, Anastopoulos, & Reid, 1998). The resulting matrix revealed significant correlations for the Rules Breaking, Lack of Attention, Hyperactivity/Impulsivity, Lack of Social interaction problem scale and for the Internalizing, Externalizing and Total scores. Convergent validity of the specific MBC subscales was supported by significant correlations with the corresponding subscales of TRF, CBCL and ADHD Rating Scale-IV. Findings underscore the importance of taking child's settings and observer influences into account and suggest that MBC is a new promising instrument that can provide valid ratings on externalizing behavior and social problems in children when used by physical educators in school settings. (Contains 3 tables.)